Modern personal computers and workstations commonly have a system for adding additional circuit boards to the base system. These add-on circuit boards are available from many manufacturers, not just the computer manufacturers. There are three standards as follows for electrical and mechanical specifications for the most common personal computer add-on circuit boards:
1. Industry Standard Architecture (ISA). ISA circuit boards are compatible with the IBM PC, IBM PC/XT and IBM PC/AT personal computers developed by International Business Machines, Inc. and other personal computers compatible with those IBM computers. PA0 2. Extended Industry Standard Architecture (EISA). The EISA architecture is a superset of ISA. EISA compatible computers will accept ISA circuit boards but EISA compatible computers have additional performance and features for circuit boards designed to take advantage of EISA. PA0 3. MicroChannel Architecture. The MicroChannel Architecture is the design used by most of the IBM PS/2 family of computers.
There is a need in the computer industry for a host computer to be able to accept and use any of the readily available industry standard add-on circuit boards, regardless of the particular design of the host computer.
FIG. 1 illustrates a prior art circuit board compatible with EISA mechanical requirements. The circuit board 100 has edge connector fingers 102 for inserting into a connector. A sheet metal bracket 104 has a hole 106 for fastening to a computer with a screw (not illustrated).
FIG. 2 illustrates a typical prior art computer designed to accommodate industry standard add-on circuit boards such as the EISA circuit board illustrated in FIG. 1. A cover 202 has been separated from chassis 200 for visibility. The computer has a base system circuit board 204 (often called a "mother board") for interconnecting secondary circuit boards 100 (often called "daughter boards"). Daughter boards compatible with the above standards have electrical connecting fingers along one edge (as illustrated in FIG. 1) and the mother board has a compatible connector 206 (FIG. 2) for accepting the daughter board edge fingers. Metal bracket 104 is attached to a metal shelf 208 by a screw (not illustrated) through a bracket hole 106. The metal bracket 104 fills an opening in the back of the computer housing. The daughter board 100 may have connectors which protrude through the metal bracket 104 for external cables. To remove or insert a circuit board with edge connector fingers, the circuit board must be moved in the direction of the edge connector fingers, as illustrated by arrow 210 in FIG. 2. External cables must be removed to permit the metal bracket 104 and connectors to clear other parts of the computer enclosure. Insertion and removal of daughter boards also usually requires removal of a computer housing cover 202 as illustrated in FIG. 2. This usually requires removal of multiple cover fasteners. Removal of the computer cover 202 potentially exposes the user to hazardous voltages. Removal of the cover also exposes critical system components to potential damage from electro-static discharge (ESD).
For many personal computer designs, the height of the computer housing must be greater than the length of the standard metal bracket for industry standard daughter boards. The computer cannot easily be made lower in height without sacrificing compatibility with many add-on daughter boards or without sacrificing ease of removal of add-on daughter boards.
Personal computer systems require insertion and removal of printed circuit boards, for service and repair and for installing different options to satisfy user needs. A need exists for a personal computer system with convenient and rapid insertion and removal of industry standard daughter boards without requiring removal of a housing cover. In addition, a need currently exists for maintaining mechanical compatibility with industry standard daughter boards while still allowing mechanical design flexibility in the host computer. In addition, a need exists for maintaining electronic compatibility with industry standard daughter boards while still allowing electronic design flexibility in the host computer.